//! Domain Layer
//!
//! Pure business logic with no external framework dependencies.
//!
//! ## Structure
//!
//! - [`value_objects`] - Immutable domain objects (keys, constants)
//! - [`entities`] - Core business entities (MemoData, MemoError)
//! - [`ports`] - Abstract interfaces (traits) for inversion of control
//! - [`aggregates`] - Complex domain objects with business invariants
//! - [`services`] - Domain service implementations